The long-term objective is to characterize structure-function relationships of ram sperm surface domains essential to fertilization. The core experiments probe the relationship of lipid modifications, with resultant effects on protein display, and capacity of the sperm to undergo an unique membrane vesiculation associated with the acrosome reaction, that is an obligatory step in the fertilization process. We have focused on the characterization of a unique protein(s) from pig sperm which controls sperm-sperm association and thus probably aids in retention of sperm viability in the female tract. Standard purification techniques yielded proteins of related structure, probably differing in extent of posttranslational processing, and having varied bioactivity. To date, MALDI-MS, peptide mapping, and PSD sequencing has been extremely useful to our program for the verification of molecular mass of the proteins, determining the nature of the posttranslational of each. Ultimately, these methods will be essential for the final elucidation of structure.